Annexin A2 Enhances Complement Activation by Inhibiting Factor H

Factor H is a circulating protein that regulates activation of the alternative pathway (AP) of complement. Mutations and genetic variations of factor H are associated with several AP-mediated diseases, highlighting the critical role of factor H in AP regulation. AP-mediated inflammation is typically triggered by illness or tissue injury, however, and tissue injury can trigger AP activation in individuals with fully functional factor H. This suggests that factor H function is affected by local conditions within tissues. We hypothesized that inducible proteins impair the ability of factor H to locally control the AP, thereby increasing AP activation. We used purified murine factor H to immunoprecipitate binding partners from mouse kidneys. Using immunoaffinity liquid chromatography-mass spectrometry, we identified annexin A2 as a factor H binding partner. Further experiments showed that annexin A2 reduces the binding of factor H to cell surfaces. Recombinant annexin A2 impaired complement regulation by factor H and increased complement activation on renal cell surfaces in vitro and in vivo. In a murine model of acute pneumococcal otitis media, the administration of annexin A2 increased AP-mediated bacterial opsonization and clearance. In conclusion, the local production of annexin A2 within tissues suppresses regulation of the AP by factor H. Annexin A2 can contribute to AP-mediated tissue inflammation by locally impairing factor H function, but it can also improve complement-mediated bacterial clearance.

Interlaboratory study on differential analysis of protein glycosylation by mass spectrometry: the ABRF glycoprotein research multi-institutional study 2012

One of the principal goals of glycoprotein research is to correlate glycan structure and function. Such correlation is necessary in order for one to understand the mechanisms whereby glycoprotein structure elaborates the functions of myriad proteins. The accurate comparison of glycoforms and quantification of glycosites are essential steps in this direction. Mass spectrometry has emerged as a powerful analytical technique in the field of glycoprotein characterization. Its sensitivity, high dynamic range, and mass accuracy provide both quantitative and sequence/structural information. As part of the 2012 ABRF Glycoprotein Research Group study, we explored the use of mass spectrometry and ancillary methodologies to characterize the glycoforms of two sources of human prostate specific antigen (PSA). PSA is used as a tumor marker for prostate cancer, with increasing blood levels used to distinguish between normal and cancer states. The glycans on PSA are believed to be biantennary N-linked, and it has been observed that prostate cancer tissues and cell lines contain more antennae than their benign counterparts. Thus, the ability to quantify differences in glycosylation associated with cancer has the potential to positively impact the use of PSA as a biomarker. We studied standard peptide-based proteomics/glycomics methodologies, including LC-MS/MS for peptide/glycopeptide sequencing and label-free approaches for differential quantification. We performed an interlaboratory study to determine the ability of different laboratories to correctly characterize the differences between glycoforms from two different sources using mass spectrometry methods. We used clustering analysis and ancillary statistical data treatment on the data sets submitted by participating laboratories to obtain a consensus of the glycoforms and abundances. The results demonstrate the relative strengths and weaknesses of top-down glycoproteomics, bottom-up glycoproteomics, and glycomics methods.

Association of immunosuppressant-induced protein changes in the rat kidney with changes in urine metabolite patterns: a proteo-metabonomic study

The basic mechanisms underlying calcineurin inhibitor (CI) nephrotoxicity and its enhancement by sirolimus are still largely unknown. We investigated the effects of CIs alone and in combination with sirolimus on the renal proteome and correlated these effects with urine metabolite pattern changes. Thirty-six male Wistar rats were assigned to six treatment groups (n = 4/group for proteome analysis and n = 6/group for urine (1)H NMR metabolite pattern analysis): vehicle controls, sirolimus 1 mg/kg/day, cyclosporine 10 mg/kg/day, cyclosporine 10 mg/kg/day + sirolimus 1 mg/kg/day, tacrolimus 1 mg/kg/day, tacrolimus 1 mg/kg/day + sirolimus 1 mg/kg/day. After 28 days, 24 h-urine was collected for (1)H NMR-based metabolic analysis and kidneys were harvested for 2D-gel electrophoresis and histology. Cyclosporine affected the following groups of proteins: calcium homeostasis (regucalcin, calbindin), cytoskeleton (vimentin, caldesmon), response to hypoxia and mitochondrial function (prolyl 4-hydroxylase, proteasome, NADH dehydrogenase), and cell metabolism (kidney aminoacylase, pyruvate dehydrogenase, fructose-1,6-bis phosphate). Several of the changes in protein expression, confirmed by Western blot, were associated with and explained changes in metabolite concentrations in urine. Representative examples are an increase in kidney aminoacylase expression (decrease of hippurate concentrations in urine), up regulation of pyruvate dehydrogenase and fructose-1,6-bisphosphatase, (increased glucose metabolism), and down regulation of arginine/glycine-amidino transferase (most likely due to an increase in creatinine concentrations). Protein changes explained and qualified immunosuppressant-induced metabolite pattern changes in urine.

Acrolein inhibits cytokine gene expression by alkylating cysteine and arginine residues in the NF-kappaB1 DNA binding domain

Cigarette smoke is a potent inhibitor of pulmonary T cell responses, resulting in decreased immune surveillance and an increased incidence of respiratory tract infections. The alpha,beta-unsaturated aldehydes in cigarette smoke (acrolein and crotonaldehyde) inhibited production of interleukin-2 (IL-2), IL-10, granulocyte-macrophage colony-stimulating factor, interferon-gamma, and tumor necrosis factor-alpha by human T cells but did not inhibit production of IL-8. The saturated aldehydes (acetaldehyde, propionaldehyde, and butyraldehyde) in cigarette smoke were inactive. Acrolein inhibited induction of NF-kappaB DNA binding activity after mitogenic stimulation of T cells but had no effect on induction of NFAT or AP-1. Acrolein inhibited NF-kappaB1 (p50) binding to the IL-2 promoter in a chromatin immunoprecipitation assay by >99%. Using purified recombinant p50 in an electrophoretic mobility shift assay, we demonstrated that acrolein was 2000-fold more potent than crotonaldehyde in blocking DNA binding to an NF-kappaB consensus sequence. Matrix-assisted laser desorption/ionization time-of-flight and tandem mass spectrometry demonstrated that acrolein alkylated two amino acids (Cys-61 and Arg-307) in the DNA binding domain. Crotonaldehyde reacted with Cys-61, but not Arg-307, whereas the saturated aldehydes in cigarette smoke did not react with p50. These experiments demonstrate that aldehydes in cigarette smoke can regulate gene expression by direct modification of a transcription factor.

Comparison of lung proteome profiles in two rodent models of pulmonary arterial hypertension

We studied the lung proteome changes in two widely used models of pulmonary arterial hypertension (PAH): monocrotaline (MCT) injection and chronic hypoxia (CH); untreated rats were used as controls (n = 6/group). After 28 days, invasive right ventricular systolic pressure (RVSP) was measured. Lungs were immunostained for alpha-smooth muscle actin (alphaSMA). 2-DE (n = 4/group) followed by nano-LC-MS/MS was applied for protein identification. Western blotting was used additionally if possible. RVSP was significantly increased in MCT- and CH-rats (MCT 62.5 +/- 4.4 mmHg, CH 62.2 +/- 4.1 mmHg, control 25.0 +/- 1.7 mmHg, p<0.001). This was associated with an increase of alphaSMA positive vessels. In both groups, there was a significantly increased expression of proteins associated with the contractile apparatus (diphosphoHsp27 (p<0.001), Septin2 (p<0.001), F-actin capping protein (p<0.01), and tropomyosin beta (p<0.02)). In CH, proteins of the nitric oxide (Hsc70; p = 0.002), carbon monoxide (biliverdin reductase; p = 0.005), and vascular endothelial growth factor (VEGF) pathway (annexin 3; p<0.001) were significantly increased. In MCT, proteins involved in serotonin synthesis (14-3-3; p = 0.02), the enhanced unfolded protein response (ERp57; p = 0.02), and intracellular chloride channels (CLIC 1; p = 0.002) were significantly elevated. Therefore, MCT- and CH-induced vasoconstriction and remodeling seemed to be mediated via different signaling pathways. These differences should be considered in future studies using either PAH model.

Analysis of 25 underivatized amino acids in human plasma using ion-pairing reversed-phase liquid chromatography/time-of-flight mass spectrometry

Amino acids in biological fluids have previously been shown to be detectable using liquid chromatography/electrospray ionization mass spectrometry (LC/ESI-MS) with perfluorinated acids as ion-pairing agents. To date, these studies have used precursor mass, retention time and tandem mass spectrometry (MS/MS) to identify and quantify amino acids. While this is a potentially powerful technique, we sought to adapt the method to time-of-flight (TOF)MS. A new application of a recently described liquid chromatographic separation method was coupled with TOFMS to employ accurate mass for qualitative identification; resulting in additional qualitative data not available with standard single quadrupole data. In the current study, we evaluated 25 physiological amino acids and one dipeptide that are routinely quantified in human plasma. Accuracy and precision of the method was evaluated by spiking human plasma with a mix of the 25 amino acids; in addition, the inclusion of a cation-exchange cleanup step was evaluated. The calibration curves were linear over a range from 1.56 to 400 microM. The dynamic range was found to be within physiological levels for all amino acids analyzed. Accuracy and precision for most of the amino acids was between 80-120% spike recovery and <10% relative standard deviation (RSD). The LC/MS technique described in this study relies on mass accuracy and is suitable for the quantitation of free amino acids in plasma.

Matrix-assisted laser desorption of peptides and proteins on a quadrupole ion trap mass spectrometer

The use of ultraviolet matrix-assisted laser desorption (MALD) to ionize peptides and proteins for analysis in a quadrupole ion trap is described. An ion source was modified to accommodate a fiber optic to transmit laser radiation from a nitrogen laser (337 nm) to the tip of the sample probe containing peptide or protein samples in a matrix of 2,5-dihydroxybenzoic acid (DHB) or 3,4-dimethoxy-4-hydroxy-cinnamic acid. Detection limits are demonstrated with 10 fmol of sperm-whale myoglobin. The dimer of sperm-whale myoglobin was also observed at m/z 34,430. A comparison is made of the tandem mass spectrum of (MS/MS) of human angiotensin I desorbed by MALD to that of the peptide desorbed by liquid secondary-ion mass spectrometry. Both spectra were found to contain abundant structural information.